1. Field of the Invention
The present invention relates in general to a magnetic sensor used in a magnetic disk drive and more specifically to an improved lead overlay magnetic sensor.
2. Description of the Background Art
Disk drives using magnetic recording of digital information are used to store most of the information in contemporary computer systems. A disk drive typically has a housing with at least one rotatable magnetic disk having a plurality of concentric tracks of magnetically stored data. There is at least one recording head typically with a separate write element and read element for writing and reading data on the tracks. The recording head is constructed on a slider and the slider is attached to a suspension. The suspension is connected to an actuator which positions the recording head over a specific track of interest. The actuator first rotates to seek the track of interest and after positioning the recording head over that track maintains the recording head in close registration to that track.
The read element in most disk drives is a sandwich structure of thin films in which the resistance is modulated by spin dependent electron transport. One common configuration of a read element is a current-in-plane (CIP) spin valve design. Another configuration of a read element is a current-perpendicular-to-plane (CPP) magnetic tunnel junction design. In general, read elements have a pinned ferromagnetic structure in close proximity to a free ferromagnetic layer. The direction of magnetization in the pinned ferromagnetic layer is fixed, or pinned, in a specified direction by an adjoining antiferromagnetic layer. The direction of magnetization in the free layer is responsive to the external magnetic field to which the read element is subjected. The magnetization in the free layer is usually partially stabilized with adjacent permanent magnets. The relative directions of the magnetization in the pinned layer and the free layer determines the resistance of the read element. Usually, tantalum is used in the uppermost layer in the read element sandwich structure to protect the other materials.
The recording density of digital information for each new generation of disk drive products is usually higher than for the previous generation. Thus, each new read element is generally required to be smaller and more sensitive. Lead overlay read elements have been developed to achieve smaller sensors with greater sensitivity. In lead overlay read elements the electrical leads overlap portions of the sandwich of layers in the sensor. This structure has at least two advantages. One, the magnetic trackwidth is defined primarily by the distance between the two leads. The second advantage of lead overlay read elements is that the less sensitive regions of the sensor adjacent to the permanent magnets are de-emphasized.
One problem with the lead overlay read element is that after deposition the tantalum layer tends to oxidize during subsequent processing. This oxidation layer can cause poor electrical connection (high contact resistance) between the layers in the sensor and the leads. This poor electrical connection can lead to a magnetic trackwidth which is substantially wider than the width defined by the leads. High contact resistance between the leads and the sensor also increases the overall sensor resistance resulting in poor recording performance.
From the foregoing it is apparent that an improved lead overlay magnetic sensor is needed with very low resistance between the leads and the sensor.